Terrible Performance while Mouse Down

I'm seeing a large spike in CPU when I hold the mouse button down. It causes rendering & overhead time to increase, even though the scene's rendering complexity hasn't changed. I presume something funny is happening with the mouse raycasting, but I don't know what:



Unity Beta 5.4b22 x64, DirectX 11, Windows 10 x64. CPU spike happens when the mouse is down, and immediately clears when the mouse button returns.

I'm relatively new to Unity, so I'm...

Terrible Performance while Mouse Down